Because ipv6 is not a simple addition, but a complex suite of new protocols meant to replace v4, except that is never going to happen in our lifetimes.
v6 should've simply been v4 with more bits
v6 should've simply been v4 with more bits
We've been deploying IPv6 for at least 10 years and have hosts that are exclusively IPv6. Then along comes Docker and Kubernetes with their retro IPv4 only stack and now customer wonder why we're struggling to make containers work or suppliers that can't understand why we can't easily deploy the latest version of their software, which is only distributed as a Docker image.
Yes, the network effects are strong with this one.
But soon. Bit by bit, I hope the true dualstack will come, and then the v4 will fade away over generations.
Dual stack are not really needed and usually add complexity for few little benefits.
The main problem of IPv6 is the lack of people willing to learn it, teach it and adopt it.
Something brand new like Kubernetes should have from the start been IPv6 only , with IPv4 at the egress parts only.